Variational formulations for nonlinear wave propagation and unsteady transonic flow

A variational principle developed recently for constrained vector fields is applied to nonlinear waves and to unsteady, transonic flow. The mathematical conditions on the admissible functional form of the speed of propagation is compatible with physical considerations for the first systems and the treatment of the mixed derivative is indicative for a proper way to discretize the second for numerical calculations. The variational formulation provides a framework for stability analysis and finite element approximations for the nonlinear systems considered.

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Zusammenfassung Ein Variationsprinzip, das in letzter Zeit für Vektorfelder mit einschränkenden Bedingungen entwickelt worden ist, wird auf nichtlineare Wellen und auf nichtstationäre transonische Strömung angewendet. Die mathematische Bedingung für die zulässige funktionale Form der Fortpflanzungsgeschwindigkeit ist verträglich mit den physikalischen Bedingungen für das erste System, und die Behandlung der gemischten Ableitung deutet an, wie das zweite System für numerische Behandlung diskretisiert werden soll. Die variationale Formulierung gibt einen Rahmen für eine Stabilitätsuntersuchung und für eine Näherung durch finite Elemente für das nichtlineare System.

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Work partially supported by Grant AFOSR-73-2561.     

Assessment of Luminescent Downshifting Layers for the Improvement of Light‐Harvesting Efficiency in Dye‐Sensitized Solar Cells

Luminescence downshifting (LDS) of light can be a practical photon management technique to compensate the narrow absorption band of high‐extinction‐coefficient dyes in dye‐sensitized solar cells (DSSCs). Herein, an optical analysis on the loss mechanisms in a reflective LDS (R‐LDS)/DSSC configuration is reported. For squaraine dye (550–700 nm absorption band) and CaAlSiN₃:Eu²⁺ LDS material (550–700 nm emission band), the major loss channels are found to be non‐unity luminescence quantum efficiency (QE) and electrolyte absorption. By using an ideal LDS layer (QE=100 %), a less absorbing electrolyte (Co‐based), and antireflection coatings, approximately 20 % better light harvesting is obtained. If the absorption/emission band of dye/LDS is shifted to 800 nm, a maximal short‐circuit current density (J_sc) of 22.1 mA cm^?2 can be achieved. By putting the LDS layer in front of the DSSC (transmissive mode), more significant loss channels are observed, and hence a lower overall efficiency than the R‐LDS configuration.     

In silico analysis of a few dietary phytochemicals as potential tumor chemo-sensitizers

P-glycoprotein (P-gp) is a membrane ATP-binding cassette (ABC) transporter that extrudes different xenobiotics out of cells. Besides its tissue protection role, overexpression of P-gp on the surface of many neoplastic cells restricts the cell entry of many anti-cancer drugs, the phenomenon which is known as multidrug resistance (MDR). It has been demonstrated that MDR cells can be sensitized toward anti-cancer agents when treated with P-gp inhibitors/modulators known as chemo-sensitizers. Due to the clinical significance and also considering the fact that many P-gp inhibitors are transported by P-gp, the search for more potent and low toxic non-transported chemo-sensitizers is an active area of research. Regarding this, several naturally occurring compounds were reported as MDR reversal agents, a category which is generally referred to as “fourth-generation P-gp inhibitors.” Dietary supplements containing natural products are widely used, and it is possible that they interact with co-administered pharmaceutical substances that are P-gp substrates, leading to altered pharmacokinetic profile. In silico approaches for quantitative and quantitative prediction of binding mechanism of dietary natural products to P-gp may be regarded as appropriate strategy in the early phase of drug discovery projects since they describe structural features of various phytochemicals for interaction with P-gp and pave the way toward alternative and novel anti-MDR scaffolds. In the present contribution, some phytochemicals of turmeric, black pepper, and green tea as commonly consumed dietary sources were subjected to systematic combined in silico analysis including molecular docking and amino acid decomposition analysis through B3LYP functional in association with 6-31G basis set. On the basis of major identified drug binding sites within P-gp internal pocket, modeled natural compounds were categorized as substrate, inhibitor, or modulator while structure binding relationship of each category was developed and elucidated.     

Mixed‐Halide CH3NH3PbI3−xXx (X=Cl,Br, I) Perovskites: Vapor‐Assisted Solution Deposition and Application as Solar Cell Absorbers

There have been recent reports on the formation of single‐halide perovskites, CH₃NH₃PbX₃ (X=Cl, Br, I), by means of vapor‐assisted solution processing. Herein, the successful formation of mixed‐halide perovskites (CH₃NH₃PbI_3?xX_x) by means of a vapor‐assisted solution method at ambient atmosphere is reported. The perovskite films are synthesized by exposing PbI₂ film to CH₃NH₃X (X=I, Br, or Cl) vapor. The prepared perovskite films have uniform surfaces with good coverage, as confirmed by SEM images. The inclusion of chlorine and bromine into the structure leads to a lower temperature and shorter reaction time for optimum perovskite film formation. In the case of CH₃NH₃PbI_3?xCl_x, the optimum reaction temperature is reduced to 100 °C, and the resulting phases are CH₃NH₃PbI₃ (with trace Cl) and CH₃NH₃PbCl₃ with a ratio of about 2:1. In the case of CH₃NH₃PbI_3?xBr_x, single‐phase CH₃NH₃PbI₂Br is formed in a considerably shorter reaction time than that of CH₃NH₃PbI₃. The mesostructured perovskite solar cells based on CH₃NH₃PbI₃ films show the best optimal power conversion efficiency of 13.5 %, whereas for CH₃NH₃PbI_3?xCl_x and CH₃NH₃PbI_3?xBr_x the best recorded efficiencies are 11.6 and 10.5 %, respectively.     

First principle study of hydrogen storage on the graphene-like aluminum nitride nanosheet

Employing density functional calculations including an empirical dispersion term, we investigated the hydrogenation of an aluminum nitride nanosheet (h-AlN) with atomic and molecular hydrogen. It was found that atomic H prefers to be adsorbed on an N atom rather than Al, releasing energy of 21.1 kcal/mol. The HOMO/LUMO energy gap of the sheet is dramatically reduced from 107.9 to 44.5 kcal/mol, upon the adsorption of one hydrogen atom. The adsorption of atomic H on the h-AlN presents properties which are promising for nanoelectronic applications. The molecular H₂ was found to be adsorbed collinearly on an N atom and dissociated to two H atoms on Al–N bond. Calculated barrier and adsorption energies for this dissociation process are about +18.9 and ?1.9 kcal/mol. We predict that each nitrogen atom in an AlN sheet can adsorb two hydrogen molecules on opposite sides of the sheet, and thus the gravimetric density for hydrogen storage on AlN sheet is evaluated to be about 8.9 wt%.     

Nonlinear-forced vibrations of piezoelectrically actuated viscoelastic cantilevers

This paper aims to study the nonlinear-forced vibrations of a viscoelastic cantilever with a piecewise piezoelectric actuator layer on its top surface using the method of Multiple Scales. The governing equation of motion is a second-order nonlinear ordinary differential equation with quadratic and cubic nonlinearities which appear in stiffness, inertia, and damping terms. The nonlinear terms are due to the piezoelectricity, viscoelasticity, and geometry of the system. Forced vibrations of the system are investigated in the cases of primary resonance and non-resonance hard excitation including subharmonic and superharmonic resonances. Analytical expressions for frequency responses are derived, and the effects of different parameters including damping coefficient, thickness to width ratio of the beam, length and position of the piezoelectric layer, density of the beam, and the piezoelectric coefficient on the frequency-response curves are discussed for each case. It is shown that in all these cases, the response of the system follows a softening behavior due to the existence of the piezoelectric layer. The piezoelectric layer provides an effective tool for active control of vibration. In addition, the effect of the viscoelasticity of the beam on passive control of amplitude of vibration is illustrated.     

Fault-Tolerant Design of a Shift Register at the Nanoscale Based on Quantum-dot Cellular Automata

Quantum-dot Cellular Automata (QCA) as a novel technology in the nanometer scale has been considered as one of the substitutes to CMOS technology. The QCA helps to create faster computers with lower power consumption. On the other hand, a shift register as one of the most important logical circuit in the digital systems consists of a line of latches. Also, the QCA-based designs have more advantages compared to the conventional CMOS designs. However, some deposition defects are possible to occur in the QCA-based designs, which have necessitated the fault-tolerant structures. Therefore, this paper aims to design an optimized 2-bit universal shift register based on QCA technology through the optimized multiplexer and D flip-flop. This paper studies the functionality and the fault tolerance of the proposed universal shift register in the presence of the QCA deposition faults. The structure of the 2-bit universal register is extendable to 4-bit, 8-bit and higher. The proposed design has better performance regarding fault tolerant, complexity and area consumption compared to the current designs based on the achieved results via QCADesigner.     

Designing a New 4:2 Compressor Using an Efficient Multi-Layer Full-Adder Based on Nanoscale Quantum-Dot Cellular Automata

Quantum-dot Cellular Automata (QCA) is novel prominent nanotechnology. It promises a substitution to Complementary Metal–Oxide–Semiconductor (CMOS) technology with a higher scale integration, smaller size, faster speed, higher switching frequency, and lower power consumption. It also causes digital circuits to be schematized with incredible velocity and density. The full adder, compressor, and multiplier circuits are the basic units in the QCA technology. Compressors are an important class of arithmetic circuits, and researchers can use quantum compressors in the structure of complex systems. In this paper, first, a novel three-input multi-layer full-adder in QCA technology is designed, and based on it, a new multi-layer 4:2 compressor is presented. The proposed QCA-based full-adder and compressor uses an XOR gate. The proposed design offers good performance regarding the delay, area size, and cell number comparing to the existing ones. Also, in this gate, the output signal is not enclosed, and we can use it easily. The accuracy of the suggested circuits has been assessed with the utilization of QCADesigner 2.0.3. The results show that the proposed 4:2 compressor architecture utilizes 75 cell and 1.25 clock phases, which are efficient than other designs.

     

Double-diffusivity heat generation effects on bioconvection process embedded in a vertical porous surface with variable fluid properties

Journal of Thermal Analysis and Calorimetry - The present paper concerns the bioconvective flow, mass and heat transfer including motile microorganisms on a vertical surface saturated with porous...